There is only one file type that uses the .TUB extension:
PaintShop Pro Picture Tube
File used by PaintShop Pro, a graphics editing program; contains graphics that can be painted repeatedly without drawing the actual objects; may include fish, plants, butterflies, and other images; painted like a paint brush, but draws images instead of paint.
NOTE: The images in TUB files can be extracted using TubeEx.
Updated: September 29, 2015